Beneficiation of low grade magnesite ores



United States Patent G BENEFICIATION F LOW GRADE MAGNESITE ORES ArthurJ. Weinig, Golden, and James F. McIntosh, Denver, Colo, assignors toBasic Incorporated, a corporation of Ohio Application December 10, 1953,Serial No. 397,372 8 Claims. (Cl. 209-466) Our invention relates to aprocess for the treatment of magnesium, refractory-type ores by frothflotation in such manner as to yield a concentrate suitable for use informin refractory compositions.

Magnesite ores have in the past been subjected to froth flotation topurify the ore sufiiciently for the production of metallic magnesium. Insuch processes considerable care has been required to eliminate, insofaras possible, the naturally occurring impurities, such as silicacompounds, limestone, alumina compounds, and the like, with the resultthat the cost of the process has necessarily been relatively high. Thecost of these processes is further accentuated by the grindingcharacteristics of the material which are such as to yield appreciablequantities of ultra-fine material which must be eliminated, as byscalping, prior to froth flotation if excessive reagent consummation isto be avoided.

According to the present invention We have discovered an economical,efiicient process for treating low grade magnesium refractory-type ores.Such ores are of the brucite-magnesite type which are soft, easilyground, and contain such siliceous impurities as serpentine, feldspar,mica, silica, talc, etc. Our process refines the low grade ore toproduce a calcined magnesium refractory containing less than about fivepercent silica. A minor amount, i. e., less than five percent, andpreferably l2 /2%, of silica is not detrimental in the calcine, since acertain amount of silica to form a frit is required. Higher siliceouscontaminants, however, are detrimental and must be removed to provide asatisfactory refractory from such low grade ore. In calcining, abouthalf the weight is lost as carbon dioxide and Water. Thus if head ore iscalcined the sinter would run about 6% silicon dioxide, or in instances,even more.

A typical analysis of the low grade ores is:

Percent Si0 3.0 CaO 3.5 MgO 40.0 R 0 1.0 HClO insoluble 3.5 Water andcarbon dioxide; "Balance Note that the perchloric acid insoluble amountincludes the silicon dioxide amount already listed. This type of ore islow in lime, and may contain substantial amounts of brucite. Generally,magnesite ores contain dolomite as the principal contaminant. The largeamounts of brucite substantially change the characteristics of the ore,especially as to flotation beneficiation. The normal procedures for thepurification of magnesite are not satisfactory for the brucite-magnesiteores.

One of the principal objects of our invention is the provision of aninexpensive process and collector reagents for treating low gradebrucite-magnesite ore in such manner as' to yield a concentrate suitablefor use in the fabrication of refractories.

Another important object of our invention is to provide 2,8315% PatentedApr. 22, 1958 ice i collector reagents for use in the process of thetype described which are relatively insensitive to the presence ofslimes or ultra-fine particles.

A further object of our invention is the provision of a process of thetype described, wherein a substantial por tion of the impuritiesnaturally present are eliminated, and some being allowed to remain withthe concentrate to assist in the formation of a binder for therefractory composition during subsequent processing. 1

Additional objects of our invention, which refer to various novelreagents and methods of treatment, Will be disclosed in the followingdetailed description and in the appended drawings, in which:

Fig. 1 is a diagrammatic illustration of a suitable flow sheetincorporating our invention; and

Fig. 2 is a diagrammatic illustration of a modified form of flow sheetincorporating our invention.

In one form of the invention, we grind our ore, which is mined in NyeCounty, Nevada, to approximately minus 200 mesh. The ore must be finelyground so as to separate the impurities. One impurity is serpentinewhich is dispersed throughout the ore, and only by grinding to such finesizes will the process be eflicient, economical, and provide a highyield. Preferably, the ore is ground to minus 200 mesh, which providesfor substantial separation of the constituents of the ore. The grind tominus 200 mesh gives substantial quantities of ground ore which is about300 mesh or finer. Since the brucitemagnesite ore is very soft, thegrinding is easy. A pulp of the ground ore is then subjected to a mildfroth flotation treatment which eliminates from the pulp the easilyfloated portion of the siliceous contaminants such as the various formsof talc and chloritic minerals. We then add to the pulp, preferably bystages, a magnesium material collector reagent, and subject the pulp tofroth flotation, with the result that a refractory grade magnesiummaterial, together with a small proportionof silica is concentrated inthe froth overflow. The excess silica contaminant, which isusually ingranular form, and the excess calcite, dolomite, etc. and a small amountof magnesite is discharged from the froth flotation stages as tailings.By proper control of reagent addition and processing, the quantities ofcalcium and silica-bearing contaminants collected in the concentratemaybe controlled in such manner that they willpermit additions andadjustments to form a suitable binder for the refractory duringsubsequent processing.

If desired, the ore, after grinding, may be classified prior to frothflotation and only the classifier underflow is subjected to frothflotation, since it has been found that in some ores the classifieroverflow is high enough in silicon dioxide forrejection as a tailing.Also, if desired, the magnesium material flotation stage may be dividedinto primary and scavenger units separated by a classifier. The overflowor fines of this classifier may be discharged from the system withoutfurther processing, while the underflow, containing the relativelycoarser particles, is subjected to further froth flotation in thescavenger unit, the concentrate from this unit being recycled to theprimary flotation cells and the underflow discharged as tailings fromthe process.

Referring to the drawings, we have illustrated in Fig. 1 a typical flowsheet, wherein brucite-magnesite ore of the type obtained near the townof Gabbs in Nye County, Nevada, is fed in conventional manner to a ballmill 10 with water and discharged into a suitable Dorr or Akinsclassifier 11, wherein the ore pulp is classified into a coarse fractionand a fine fraction. If brucite is present in the ore, the pulp willhave a pH .of about 8.5. The portion of the ore coarser thanapproximately 200 mesh is recycled through the ball mill 10, while theminus 200'mesh fraction is discharged from the classifier 11 to a secondclassifier 12, which is a hydro separator or a bowl classifier.

The classifier 12 divides the ore into two approximately equal portions,one portion being plus about 300 mesh and the other being minus about300 mesh. The coarser, or plus 300 mesh, is discharged into a primarycoarse brucite-magnesite froth flotation unit 13, it being understoodthat each froth flotation unit may include several cells. A suitablebrucite-magnesite collector reagent is added to the pulp, preferably bystages during passage of the pulp through the primary flotation unit 13,with the result that the relatively coarse brucite-magnesite particlesare collected and concentrated in the froth overflow of the flotationunit 13.

The underflow or tailings from the primary flotation cells 13 isdischarged through a scavenger flotation unit 14 of similar design,where additional magnesium material collector reagent may be added. Mostof the remaining magnesium material is concentrated in the frothoverflow of the flotation cells 14 and are recycled for passage throughthe primary unit 13 in conventional manner. The underflow from the unit14 is discharged from the system as tailing reject.

The overflow of the classifier 12 is passed through a silica frothflotation unit 16, limited quantities of a suitable silica collectorreagent being added, preferably by stages, in this operation. The effectof this flotation stage is to concentrate in the froth overflow of theunit 16 the easily floated portions of the silica contaminants naturallypresent in the ore and which concentrate largely in the overflow of theclassifier 12. These easily floated particles are usually silicaminerals having a relatively flaky, rather than granular, form, andinclude the various talc and some chloritic minerals commonlyencountered in the type of ore described. The underflow from theflotation unit 16 contains the magnesite values and is discharged into afine magnesite froth flotation unit 17, where suitable magnesitecollector reagents are added, preferably by stages.

This stage of the operation concentrates in the froth overflow themagnesium minerals in the fine portion of the ore. It will be found,however, that the brucitemagnesite collector reagent employed alsocollects and floats a small proportion of the calcium-bearing mineralsnaturally present. Calcium carbonate, or calcite, and dolomite are thepredominant minerals in this category. Also since the pulp containslimited quantities of the silica collector reagent added in the unit 16,it will be found that a small quantity of silica is also incorporated inthe froth concentrate. When the quantity of collector reagent added inthe unit 16 is properly gauged and the units 16 and 17 operated inaccordance with the teachings of this invention, it will be found thatthe calcium-bearing and silica-bearing minerals incorporated in theoverflow from the unit 17 will be in such proportion as to permitadjustments and additions to form a suitable binder during futureprocessing of the concentrate. The underflow from the unit 17 containsthe unfloated silicabearing minerals of the fine fraction of the groundore, these usually being granular in nature, together with a certainamount of dolomite, calcite, and other impurities and are discharged asa reject tailing.

In Fig. 2, we have illustrated a somewhat modified process, wherein oreof the type described is fed in conventional manner to a ball mill 18and discharged as an aqueous pulp into a classifier 19, similar toclassifier 11.

In this process, the classifier 19 may be operated in such manner as torecycle plus 325 mesh ore particles to the ball mill 18 for furthergrinding, While the underflow from the classifier 19 is discharged to asilica froth flotation unit 21, similar to the unit 16, previouslydescribed.

A suitable silica collector reagent is added at this point, preferablyby stages, and the easily floated portion of the silica contaminantspresent in the ore discharged as a froth reject from the flotation unit21. The underflow from theunit, 21 contains a substantial portion of theFire p int F silica contaminants present, together with thebrucitemagnesite ore and the calcium-bearing minerals. This underflow isdischarged to a primary magnesium material froth flotation unit 22,where suitable collector reagents are added, preferably by stages. Themagnesium values are thereby concentrated in the froth overflow from theflotation unit 22, together with a portion of the silica andcalcium-bearing mineral contaminants present in the ore, this portion ofthe operation being somewhat similar to the operation of the frothflotation unit 17 previously described.

In this instance, however, the underflow from the flotation cell 22 isdischarged into a classifier 23, which is operated in such manner thatthe coarse particles are discharged into a scavenger magnesium materialfroth flotalion cell 24 for further treatment. The overflow from theclassifier 23 consists predominantly of silicate minerals and otherimpurities suitable for discharge from the system as tailing reject.

Froth concentrate produced by the scavenger battery 24 contains most ofthe remaining brucite-magnesite ore particles, the underflow consists ofundesirable impurities suitable for discharge from the process atrailings. The froth concentrate from the scavenger flotation unit 24 isrecycled through the unit 22 in conventional manner.

We have discovered a new collector for silica, which is elficient andyet inexpensive in the process for recovering magnesium values from lowgrade brucite-magnesite ores. The collector is a combination of cresylicacid (usually derived from petroleum sources) and certain high molecularweight aliphatic ammonium acetates; the first of which is known asAquaquad 12, which is a lauryl trimethyl ammonium acetate. Anothercollector reagent suitable for the combination is an amine and has ageneral chemical formula RNH acetate, in which R represents the rosinacids derived from tall oil. Still another suitable reagent for use inour collector is commercially known as Armac S, which is a variablecomposition and consists of the various saturated and unsaturated fattyacids derived from soy beans and reacted with ammonia to form aminesafter which the amines are reacted with acetic acid to form thecorresponding acetate.

The collector reagents suitable for use in the magnesium materialflotation stages include a reagent known as Armour Neo Fat S142,essentially a refined tall oil product of somewhat variable composition.A typical analysis of this reagent indicates the following approximatecomposition:

Oleic acid percent 46.0 Linoleic acid do 39.0 Linolenic acid do- 3.0Rosin acid n do- 12.0 Mean molecular weight 295.2 Iodine value (Wijs)130.0 Neutralization value 190.0

Other aliphatic carboxylic acids may be used, the choice being largelyeconomical. The tall oil product is currently less expensive than othersuitable fats or oils. If combined with a suitable frother, pure formsof the acids indicated above may be employed as magnesite collectorreageants. The cost of such acids, however, is excessive and their usetherefore is not feasible industrially.

Another tall oil derivative, commercially known as Triple DistilledIndusoil, may also be employed as a magnesium material flotationreagent. This composition, similar to Neo Fat S142, contains abietic,linoleic, and linolenic acids, usable directly or in saponified form.The characteristics of this reagent are substantially as follows:

Specific gravity at F 0.96-0.98 Saybolt viscosity at 210F 50-70 Flashpoint F 350-380 asents r i Acid number 180 Saponification number 181Fatty acids approximately percent- 57 Rosin acids approximately do 33 Inaddition to the above-described reagents, napthenic acids may also beemployed as collector reagents for magnesium materials. In the magnesiummaterial flotation, cresylic acid or a suitable substitute may beemployed as a frother. The collector reagent for the silica may bevaried to suit the particular batch of ore being processed. In general,the amine acetate may be used in amounts from 0.10 to 0.75 pound per tonof head ore, and the cresylic acid may also be varied from about 0.10 to0.75 pound 'per ton of head ore. The magnesium material collector may beused in amounts of 0.30 to 5.0 pound per ton, determined by therequirements of the ore.

To illustrate the specific application of these reagents and the flowsheets illustrated, a series of tests were run utilizing the arrangementdisclosed in Fig. 1. In these tests, Aquaquad 12 in the amount of about0.18 pound per ton of head ore were fed to the flotation unit 16 of Fig.l in stages, together with about 0.16 pound per ton of cresylic acid.About 0.15 pound of Neo Fat S142 per ton of ore were fed to theflotation unit 17. About 0.32 pound of Neo Fat S142 per ton of ore werefed to the flotation unit 13 in two equal stages, and 0.35 pound per tonof ore of the same reagent were added in two stages to the scavengerunit 14. The results of the beneficiation were as follows:

Table I Percent Percent weight 1 Con. Acid Tail Insoluble Ball MillClassifier Overtlw 100.0 3. 31 Akins Classifier Course. 53. 6 2. 89Akins Classifier Fines 46. 4 3. 42 Coarse Concentrate 46. 3 1. 37 CoarseTails 7. 3 11. 52 Fines Froth Rejects... 7. 3 7.00 7. 3 FinesConcentrate 30. 0 1. 73 Fines Tails 9.1 6. 94 9.1 Calculated TotalConcentrate 76. 3 1. 51 Calculated Total Tails 23.7 8. 38

1 By timed sample.

Similarly, the following amounts of reagent were added as indicated inthe circuit shown in Fig. 2. About 0.40 pound and about 0.11 pound ofRNH acetate (where R represents rosin acids) and cresylic acids,respectively, per ton of head ore is added to the pulp in the scalpercircuit 21. The magnesium material in the primary circuit 22 is floatedby adding about 0.25 pound of Triple Distilled Indusoil per ton of ore,and, also, by adding about 0.43 pound of the Triple Distilled Indusoilto the scavenger circuit 24. The collector is added in three equalstages to the primary magnesium material circuit, and in two equalstages in the scavenger circuit. The results of the flotation aresimilar to the results shown in Table I, and are as follows:

The Mg concentrate will yield a calcine of 3% Si0 or less since theinsoluble matter is somewhat higher in value than pure SiO Whilespecific examples have been utilized to fully de* scribe the invention,there is no intent to limit the scope thereof to the precise details soset forth, except insofar as defined by the following claims.

We claim:

1. in the art of concentrating magnesium material from brucite-magnesiteores, the steps of reducing such an ore to a finely divided condition inwhich a substantial portion is in the size range of less than about 300mesh, forming a free flowing pulp of said finely divided ore having a pHof about 3.5, subjecting said pulp to a froth flotation treatment in thepresence of a silica collector reagent comprising crecylic acid and ahigh molecular weight aliphatic amine acetate for the froth flotationremoval of a substantial portion of siliceous contaminants from thepulp, and subjecting the silica-depleted pulp to a second frothflotation treatment in the presence of a collector reagent for magnesiummaterials whereby to obtain a magnesium material concentrate containingabout 1-2 /z% silica by weight.

2. In the art of concentrating magnesium material from brucite-magnesiteores, the steps of reducing the ore to a finely divided condition inwhich a substantial portion will be in the size range of less than about300 mesh, forming a free flowing pulp of said finely divided ore havinga pH of about 8.5, subjecting said pulp to a froth flotation treatmentin the presence of a silica collector reagent comprising cresylic acidand a compound of the formula RNH Ac, where R is selected from lauryltrimethyl, and rosin acids for the removal of a substantial portion ofsiliceous contaminants of the pulp, and subjecting the silica-depletedpulp to a second froth flotation treatment in the presence of analiphatic carboxylic acid as a collector reagent for magnesium material,whereby to obtain a magnesite concentrate containing 1-2 /z% silica byweight.

3. In the art of concentrating magnesium material from brucite-magnesiteores, the steps of reducing the ore to a finely divided condition inwhich a substantial portion will be in the size range of less than afree flowing pulp of said finely divided ore having a pH of about 8.5,subjecting said pulp to a froth flotation treatment in the presence of asilica collector reagent comprising cresylic acid and a compound of theformula RNH Ac, where R is selected from lauryl tri-methyl, and rosinacids for the removal of a substantial portion of siliceous contaminantsof the pulp, and subjecting the silicadepleted pulp to a second frothflotation treatment in the presence of a tall oil as a collector reagentfor magnesium material, whereby to obtain a magnesite concentratecontaining 1-2 /2% silica by weight.

4. In the art of concentrating magnesium material from brucite-magnesiteores, the steps of reducing the ore to a finely divided condition inwhich a substantial portion will be in the size range of less than about300 mesh, forming a free flowing pulp of said finely divided ore havinga pH of about 8.5, subjecting said pulp to a froth flotation treatmentin the presence of an eflective amount of a silica collector reagentcomprising cresylic acid and lauryl tri methyl ammonium acetate for theremoval of a substantial portion of siliceous contaminants of the pulp,and subjecting the silica-depleted pulp to a second froth flotationtreatment in the presence of a tall oil as a collector reagent formagnesium material, whereby to obtain a magnesite concentrate containing12 /2% silica by weight.

5. In the art of concentrating magnesium materials frombrucite-magnesite ores, the steps of grinding such an ore to provide afinely divided material, the major portion of which is less than about200 mesh, forming a free flowing pulp of such material having a pH ofabout 8.5, classifying the pulp constituents into minus 300 mesh andplus 300 mesh portions, passing the plus 300 mesh pulp portion directlyto a froth flotation treatment in the presence of a highmolecular-weight aliphatic acid compound about 300 mesh, forming 7 H asa collector reagent for magnesium material, passing the minus 300 meshpulp portion to a scalper flotation treat ment in the presence of acollector reagent for siliceous contaminants comprising cresylic acidand R-NH Ac, wherein R is a high molecular weight aliphatic radical, forremoval of a substantial portion of the siliceous contaminants, andsubjecting the silica-depleted pulp to a froth flotation treatment inthe presence of a high molecular weight aliphatic acid as a collectorreagent for magnesium material.

6. In the art of concentrating magnesium values from brucite-rnagnesiteores, the steps of forming a free flowing pulp of such an ore groundapproximately to minus 325 mesh and having a pH of about 8.5, subjectingsuch pulp to a froth flotation treatment in the presence of a collectorreagent for siliceous matter comprising cresylic acid and a highmolecular weight aliphatic amine acetate for removal of a substantialportion of the siliceous impurities of the ore, passing thesilica-depleted pulp to a froth flotation treatment in the presence of amagnesium material collector reagent for removal of a magnesium materialconcentrate, subjecting the residual pulp of said flotation stage to aclassification treatment for rejection of a fine tailings, subjectingthe undertlow of said classification stage to a froth flotation in thepresence of a magnesium material collector reagent, and returning theconcentrate of said latter stage as part of the feed to said initialmagnesium material flotation stage.

7. In the art of concentrating magnesium values from brucite-magnesiumores, the steps of forming a free flowing pulp of such an ore groundapproximately to minus 325 mesh and having a pH of about 8.5, subjectingsuch pulp to a froth flotation treatment in the presence of a collectorreagent for silica comprising cresylic acid and RNI-I acetate, wherein Ris a high molecular weight aliphatic radical, for removal of asubstantial portion of the siliceous content of the ore, passing thesilica-depleted pulp to a froth flotation treatment in the presence of ahigh molecular weight aliphatic acid composition as a magnesium materialcollector reagent for removal of a magnesium material concentrate,subjecting the residual pulp of said flotation stage to a classificationtreatment for rejection of a fine tailings, subjecting the underflow ofsaid classification stage to froth flotation in the presence of saidmagnesium material collector reagent, and returning the concentrate ofsaid latter stage as part of the feed to said first magnesium materialflotation stage.

8. The process of treating brucite-magnesium ores for the recovery ofmagnesium values as a concentrate of the treatment, which comprisesforming an aqueous pulp of such an ore having a major portion of itssolid content in a size range of about 3OO mesh, maintaining thecirculating pulp. of the treatment at a pH of about 8.5, and subjectingsaid pulpto a two-stage flotation separation with cresylic acid and ahigher molecular Weight, aliphatic amine introduced as a collectorreagent in one stage of, said concentration so as to collect siliceouscontent of the ore as a froth concentrate of such a separation, andintroducing a collector for the magnesium materials as a collector inanother stage of said concentration so as to concentrate the magnesiumvalues of the ore as a concentrate of said other stage.

References Cited in the file of this patent UNITED STATES PATENTSErickson Sept. 28, 1943 OTHER REFERENCES

8. THE PROCESS OF TREATING BRUCITE-MAGNESIUM ORES FOR THE RECOVERY OFMAGNESIUM VALUES AS A CONCENTRATE OF THE TREATMENT, WHICH COMPRISESFORMING AN AQUEOUS PULP OF SUCH AN ORE HAVING A MAJOR PORTION OF ITSSOLID CONTENT IN A SIZE RANGE OF ABOUT -300 MESH, MAINTAINING THECIRCULATING PULP OF THE TREATMENT AT A PH OF ABOUT 8.5, AND SUBJECTINGSAID PULP TO A TWO-STAGE FLOTATION SEPARATION WITH CRESYLIC ACID AND AHIGHER MOLECULAR WEIGHT, ALIPHATIC AMINE INTRODUCED AS COLLECTOR REAGENTIN ONE STAGE OF SAID CONCENTRATION SO AS TO COLLECT SILICEOUS CONTENT OFTHE ORE AS A FROTH CONCENTRATE OF SUCH A SEPARATION, AND INTRODUCING ACOLLECTOR FOR THE MAGNESIUM MATERIALS AS A COLLECTOR IN ANOTHER STAGE OFSAID CONCENTRATION SO AS TO CONCENTRATE THE MAGNESIUM VALUES OF THE OREAS A CONCENTRATE OF SAID OTHER STAGE.